A Snohomish County man has become the first person in Washington state to die from complications of swine flu, health officials announced Saturday.

The death is only the third in the U.S. from the flu; the other two were in Texas. Forty-eight people have died from the flu in Mexico.

The Snohomish County man, who officials said was in his 30s, had an underlying heart condition. He became sick April 30 and died Wednesday from viral pneumonia, a complication from swine-origin influenza (H1N1), officials with the state Department of Health said.

Officials would not release his name nor say where in Snohomish County he lived.

State Department of Health (DOH) officials received preliminary test results Saturday from an autopsy. The announcement came at the DOH’s offices in Shoreline.

Dr. Gary Goldbaum, Snohomish Health District medical director, provided no details on how or where the man who died might have caught the virus. The man had seen a doctor and was on anti-virus medication.

“We don’t have any risk factors established for him,” Goldbaum said. “The virus is now, we believe, widespread through the community. He could have been exposed here.”

The swine flu so far has struck mostly children and has caused generally mild illnesses. For instance, three-fourths of the 70 confirmed King County cases were age 19 or younger. Only three required hospitalization.

Dr. Tony Marfin, state communicable-disease epidemiologist with the DOH, offered a possible explanation for the fact that most of those who have so far caught the flu have been young.

“Older people may have some immunity they gained many, many years ago being exposed to a similar virus,” he suggested.

But he also was quick to point out that, unlike the most deadly flu outbreak in U.S. history in 1918, most of the adults who’ve died in this outbreak also had some underlying health condition.

State Secretary of Health Mary Selecky, asked if the public perception that the swine-flu threat was diminishing was now proven wrong, urged an “appropriate level of concern.” She defined that as washing hands, covering coughs and sneezes and staying home if you develop flu symptoms.

“So far we have not seen reduced activity with this flu in this state or around the country,” Selecky said. “This is a new virus and we’re watching it very closely.

“We do want the public to know we are being vigilant,” she said. “The best anyone can do is avoid getting or spreading the flu.”

The state is continuing to work with local and federal partners to track the outbreak, Selecky said.

“And while most illnesses from this new flu strain have been fairly mild, we must remember that influenza claims about 36,000 lives every year nationwide. That’s why we urge people to take this outbreak, and the seasonal flu we see every year, very seriously,” she said.

Earlier Saturday, the Health Department announced that an additional 18 cases of swine flu have been confirmed in Washington, bringing the state’s total to 101. The DOH said another 19 cases are considered probable for swine flu.

As of Saturday, 70 cases were confirmed in King County; 18 were confirmed in Snohomish County; five in Pierce County; two each in Spokane, Whatcom and Clark counties; and one each in Thurston and Skagit counties.

The probable cases include 10 in King County and nine in Snohomish County.

The illness prompted several Seattle-area schools to close, but all have since reopened.

The new H1N1 strain of swine flu has been similar to seasonal flu in symptoms, spread and response to treatment. Typically, people with existing health conditions are at greater risk of serious health effects from influenza.

More than 4,100 are sick from swine flu in 29 countries. Those are much lower numbers than were feared at the start, based on early reports of an aggressive and deadly flu in Mexico.

The two swine-flu deaths in Texas — a Mexican toddler and a pregnant woman — each suffered from several other illnesses when they were infected with the virus, the Centers for Disease Control and Prevention (CDC) said.

Miguel Tejada Vazquez, 21 months, had a chronic muscle-weakness condition called myasthenia gravis, a heart defect, a swallowing problem and lack of oxygen. He died during a family visit to Texas.

Judy Trunnell, 33, was hospitalized for two weeks until she died Tuesday. The teacher was in a coma, and her baby was delivered by cesarean section. She had asthma, rheumatoid arthritis and a skin condition, psoriasis.

Information from Seattle Times archives, staff reporter Kyung M. Song and The Associated Press is included in this report.